1. Field of the Invention
The present invention relates generally to waveguide switches and particularly to a waveguide switch having four ports and three connecting states.
2. Description of the Prior Art
In order to improve the reliability of communication systems, it has been the practice to provide redundant elements in the system which are switched in to replace system elements which have failed. For example, it is common to provide in a communication system standby units, such as receivers and transmitters, which are appropriately switched to replace main units that have failed.
The switching apparatus needed in such redundancy systems proved easy to provide when systems operated at low frequencies or at low transmitter power levels. But with the move to higher frequencies and power levels, existing switching apparatus has proved to be inadequate. The deficiency is particularly acute in the communication satellite area where the high cost of an orbited satellite requires the maximum possible switchable combinations of system elements, but also requires a very light and small switch.
As disclosed in pending application Ser. No. 670,290, filed Mar. 25, 1976 to Assal et al, now U.S. Pat. No. 4,070,637, the switch needed for higher order satellite system redundancy configurations is one having four ports and three connecting states, referred to as a R switch, as shown in FIG. 1. The R switch must provide minimal attenuation in the conducting paths and maximum isolation in the non-conducting paths.
Since satellite communication systems operate at very high frequencies, the R switch must be able to operate efficiently at these frequencies. As is well known in the microwave art, waveguide switches have the best electrical characteristics at these high frequencies. However, the known waveguide switch which provides the three connecting states is not suitable in satellite communication systems because of several deficiencies including excessive size, weight and cost.
A known non-waveguide switch which provides the three connecting states of the present invention is the microwave matrix switch of Lee Laboratories, Lexington, Massachusetts. This microwave matrix switch uses connectors instead of waveguide ports and, therefore, is unsuitable for satellite communication systems where low loss and high power capability are required.
A known waveguide switch called a B switch, as illustrated in FIG. 2, can provide only the first and second connecting states shown in FIG. 1. One such B switch is available from Sivers Labs in Stockholm, Sweden and is designated PM 7306J. As shown in FIG. 2, the B switch can provide the first connecting state with port 1 connected to port 2 and port 3 connected to port 4. The B switch can also provide the second connecting state with port 1 connected to port 3, and port 2 connected to port 4. The B switch cannot provide the third connecting state, since port 1 cannot be connected to port 4 simultaneously with port 2 being connected to port 3.
A known waveguide switch called the modified B switch provides the three connecting states of the present invention. As is apparent below, however, the modified B switch has several major deficiencies with respect to satellite communication systems including excessive size, weight, and cost.
A modified B switch, as shown in FIGS. 3 and 4, includes an unmodified B switch which is now described. The B switch is housed in a square structure designated generally by reference numeral 30. Ports 20, 22, 24 and 26 are provided in successive 90.degree. intervals around structure 30. For purposes of description and with reference to FIG. 2, port 20 corresponds to port 1, port 22 corresponds to port 2, port 24 corresponds to port 4, and port 26 corresponds to port 3. A structure 28, mounted for rotation on a drive shaft 10, is provided in structure 30. A waveguide 12 is mounted to structure 28 and has a length such that it can electrically couple port 22 to port 26, or port 20 to port 24 depending on the angle of rotation of shaft 10. A curved waveguide 16 is mounted to structure 28 and has a curve and length such that it can electrically couple port 20 to port 22, port 22 to port 24, port 24 to port 26, or port 26 to port 20 depending on the angle of rotation of shaft 10. Similarly, a curved waveguide 14 is mounted to structure 28 and has a curve and length such that it can electrically couple port 24 to port 26, port 26 to port 20, port 20 to port 22, or port 22 to port 24 depending on the angle of rotation of shaft 10. Obviously, with this unmodified B switch, it is impossible to provide the third connecting state of the present invention, since port 20 cannot be connected to port 24 simultaneously with the connection of port 22 to port 26.
In order to provide the third connecting state of the present invention, the B switch can be modified in the following fashion. Specifically, a waveguide 18 having four 90.degree. bends can be mounted to structure 28 perpendicular to and below waveguide 12; waveguide 18 has a length such that it can electrically couple port 20 to port 24, or port 22 to port 26 depending on the angle of rotation of shaft 10.
While the modified B switch provides the three connecting states, it has several major deficiencies. First, in order to provide waveguide 18, the height of structure 30 has to be at least doubled, and the length and width of structure 30 has to be increased to accommodate the four required 90.degree. bends in waveguide 18. In a satellite, size is extremely critical. Second, the addition of waveguide 18 requires a larger diameter shaft 10 and a larger source to drive shaft 10. In a satellite, weight is extremely critical. Third, both a modified and an unmodified B switch require close tolerance components due to rotation required to perform the switching function, and these critical dimensions resulted in added manufacturing costs.
Furthermore, there are several known waveguide switches that do not provide the three connecting states of the present invention. Specifically, a waveguide switch is disclosed in U.S. Pat. No. 2,164,792 which provides only a single-pole single-throw connecting state. A waveguide switch is disclosed in U.S. Pat. No. 3,546,633 which also provides only a single-pole single-throw connecting state. A waveguide switch is disclosed in U.S. Pat. No. 3,953,853 which provides only a single-pole double-throw connecting state. Finally, a waveguide switch is disclosed in U.S. Pat. No. 3,768,041 which also provides only a single-pole double-throw connecting state.